1. Field of the Disclosure
This disclosure generally relates to tools used in oil and gas wellbores. More specifically, the disclosure relates to downhole tools that may be run into a wellbore and useable for wellbore isolation, and methods pertaining to the same. In particular embodiments, the tool may be a frac plug or bridge plug having one or more parts made of composite drillable materials.
2. Background of the Disclosure
Oilfield drilling and production technology continues to evolve in order to attempt to meet the ever-increasing worldwide demand for valuable hydrocarbons. As reservoirs that contain hydrocarbons are typically found in layers that run parallel with the earth's crust, horizontal drilling technology was developed in order to maximize the amount of reservoir fluid accessible with a wellbore. In contrast to vertical drilling, which requires multiple vertical wellbore completions in order to produce from such a layer, only a single horizontal completion that runs through the reservoir is needed. Hence horizontal completions are inherently more efficient than vertical counterparts. The main constraint on this technology is how to drill and produce economically, as horizontal drilling is orders of magnitude costlier than vertical drilling. Thus, the industry is also continually striving to improve technology and reduce costs associated with horizontal drilling.
Among specific concerns, horizontal operations require higher pressure and faster flow rates, which tends to result in greater likelihood of parts or components of downhole tools loosening or disconnecting entirely. As a consequence of small tolerances between casing, tools, and parts of the tool, there is increased chance of catching something in the well during deployment, especially if anything is loose on the tool. This is of particular significance when it comes to deployment and operation of plugging tools.
Like horizontal drilling, fracing is a process that continues to grow in popularity, as it is known to enhance and assist production of formations. Typically, the frac process includes the use of a downhole plugging tool set in the wellbore below or beyond a respective target zone, which serves the function of being able to isolate a section of the wellbore in order to treat the zone. Isolation tools for this kind of operation are usually bodies constructed of durable metals that have a seal element made of compressible material associated therewith, where the seal element is expanded radially outward to engage the tubular and seal off a section of the wellbore. The setting of the tool is followed by pumping or injecting high pressure frac fluid into the target zone, resulting in fractures or “cracks” in the formation. The end result is the valuable hydrocarbons are more readily and easily produced through the fractures in the formation.
At present, the fundamental shift in the industry from vertical drilling to horizontal drilling has resulted in a void of technology selectively designed and useable specifically for horizontal drilling. That is, downhole tools, such as frac plugs, originally designed for vertical drilling operations are now used in horizontal operations, which ultimately means these tools do not work as well as they were designed to perform.
More problematic is that the use of plugs in a wellbore is not without other concerns, as these tools are subject to known failure modes regardless of wellbore orientation. For example, when the plug is run into the wellbore, slips have a tendency to loosen or pre-set before the plug reaches its destination, resulting in damage to the casing, as well as operational delays in order to fix the casing and/or deploy a new plug.
To combat pre-setting, operators typically wrap bailing wire (and the like) around the slips. Although this may prevent pre-setting, this has the inadvertent consequence of creating additional surfaces (i.e., surface areas) from which the tool may get caught up or catch against the tubular. Moreover, the wire is often wrapped around inserts disposed in the slip, thus rendering the inserts unable to smoothly or completely contact, and hence grip, the surrounding tubular surface. This results in unequal or inadequate load distribution during setting, and the tool is prone to being moved from the desired set position at a load far less than what it is designed for.
Frac fluid is also highly pressurized in order to not only transport the fluid into and through the wellbore, but also extend into the formation in order to cause fracture. Upon proper setting, the plug may be subjected to extreme pressure and temperature conditions, thus the plug must be capable of withstanding these conditions without destruction of either the plug or the seal formed by the seal element. High temperatures are generally defined herein as downhole temperatures above 200° F., and high pressures are generally defined herein as downhole pressures above 7,500 psi, and even in excess of 15,000 psi.
With these aspects in mind, it becomes imperative for an operator to be provided a downhole tool that can account for all of the problems associated with use of such a tool. As most problems encountered often center around the slips, the design and/or fabrication of such slips is typically the significant expense of the overall tool cost.
There are needs in the art for new and improved apparatus, systems, and methods for isolating wellbores in a viable and economical fashion. There remains a great need in the art for downhole plugging tools that form reliable engagement against a surrounding tubular, and are not subject to pre-setting. There is also a need for a downhole tool made substantially of a drillable material that is easier and faster to drill. It is highly desirous for these downhole tools to readily and easily withstand extreme wellbore conditions, and at the same time be cheaper, smaller, lighter, and useable in the presence of high pressures and flow rates associated with drilling and completion operations.